Electrochemical cyanomethylation of phenazines in acetonitrile

Cathodic reductions of phenazine (1) and 2,7-diethoxyphenazine (2) were carried out in acetonitrile containing trifluoroacetic acid (TFA) under air, and 2-(cyanomethy)phenazine (3) and 2-(cyanomethyl)-3,8-diethoxyphenazine(4) were obtained as final products, respectively. Cyclic voltammetry (CV) of 1 and 2 showed two cathodic peaks and these peaks had counterparts under N-2 and/or air, When CV was carried out under air, the current of the second cathodic peak of 2 was increased, Controlled potential electrolysis (CPE) of 1 under N, at the second cathodic peak gave a value of 1.8 for n (faradays per mole of substance electrolyzed) and 84% of the starting compound was recovered. Dihydrophenazines produced by the electrochemical reduction of 1 and 2, activated dissolved oxygen, The activated oxygen oxidized the solvent, i.e., acetonitrile, and gave a cyanomethyl radical, which attacked the 2-position of 1 and 2 to give 3 and 4, respectively, MO calculations of three putative intermediates were conducted to obtain their localization energy and heat of formation, The heat of formation of the intermediate radical appears to decide the direction of the reaction.